Blanket cylinders of offset printing machines can be an endless, cylindrical sleeve or an interrupted cover, clamped in a clamping groove. German Patent Disclosure Document DE-OS 27 08 689 describes an offset printing machine having a continuous cylindrical cover which is replaceable applied on an offset printing cylinder. Elastic materials are used for the coating.
The referenced textbook, Walenski: "Einfuhrung in den Offsetdruck" ("Introduction to Offset Printing"), published by Hanns Eggen GmbH & Co. KG, Hannover, Fed. Rep. Germany, pp. 262, 263, describes rubber blankets for use in customary offset rotary printing machines which are elastically deformable, but not volume compressible. Rubber blankets of this type are referred to as incompressible or non-compressible blankets. Only gaseous materials are volume compressible. Liquids and solid materials are not volume compressible. Rubber blankets having intermediate rubber layers of micro-compressible, volume compressible material, connected by air channels or pores, have not found acceptance in offset printing machine sleeves. Use of customary, that is, elastic but not volume compressible material, is not suitable since, in contrast to blankets which are clamped in clamping grooves, continuous sleeves do not permit release of tension or bulges which form in operation. Practical use of coated, continuous carrier sleeves, particularly for wide or axially long printing cylinders was not possible. Such sleeves could not be made, either in form of a compact inherently elastic sleeve, or as an elastic coating on a sleeve, and foamed coatings were impossible to use.
Customary materials in order to make foamed structures, such as cast polyurethane, had been considered. Yet, use of previously known volume compressible material was not economically possible, even if, theoretically, the technical use would have been possible.